U.S. patent application number 13/146900 was filed with the patent office on 2012-05-03 for wind turbine with lvrt capabilities.
Invention is credited to Georg Rudolf, Karl-Friedrich Stapelfeldt.
Application Number | 20120104754 13/146900 |
Document ID | / |
Family ID | 42320324 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120104754 |
Kind Code |
A1 |
Rudolf; Georg ; et
al. |
May 3, 2012 |
WIND TURBINE WITH LVRT CAPABILITIES
Abstract
Systems and methods ("utility") for providing Low Voltage Ride
Through (LVRT) capabilities for wind turbines are disclosed. The
utility includes a directly connected synchronous generator (214)
that is designed to have a high dynamic pull-out torque. To remain
connected to the power grid (224) during low voltage events, the
utility boosts the excitation current applied to the rotor of the
synchronous generator (214). Further, the utility may include a
torque regulator in the form of d torque-regulating gearbox (210),
which in turn includes adjustable guide vanes (624) that may be
positioned to reduce the amount of mechanical torque applied to the
rotor shaft of the synchronous generator (224) during low voltage
events. Additionally, the utility may also include a braking system
(206) and a pitch control system (234) to limit the acceleration of
the wind rotor (202) shaft during low voltage events.
Inventors: |
Rudolf; Georg; (Bliestorf,
DE) ; Stapelfeldt; Karl-Friedrich; (Lubeck,
DE) |
Family ID: |
42320324 |
Appl. No.: |
13/146900 |
Filed: |
April 30, 2009 |
PCT Filed: |
April 30, 2009 |
PCT NO: |
PCT/EP09/03158 |
371 Date: |
January 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61148777 |
Jan 30, 2009 |
|
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Current U.S.
Class: |
290/44 |
Current CPC
Class: |
F05B 2270/10711
20130101; F05B 2260/70 20130101; F05B 2260/90 20130101; Y02E 40/32
20130101; H02P 2101/15 20150115; Y02E 10/763 20130101; Y02E 40/30
20130101; F03D 7/042 20130101; F03D 7/0284 20130101; F05B 2270/1016
20130101; Y02E 10/72 20130101; H01H 9/547 20130101; H02P 9/14
20130101; Y02E 10/725 20130101; Y02E 10/723 20130101; Y02E 10/76
20130101; H02J 3/1885 20130101; F05B 2220/70642 20130101 |
Class at
Publication: |
290/44 |
International
Class: |
H02P 9/10 20060101
H02P009/10 |
Claims
1. An automated method for allowing a wind turbine to remain
electrically connected to a power grid during a low voltage event,
the wind turbine comprising a synchronous generator coupled to the
power grid and to a turbine rotor through a torque regulator, the
method comprising: detecting a low voltage event; and boosting a
rotor current of the synchronous generator to provide reactive
power to the power grid during the low voltage event, wherein the
boosting step is initiated in response to the detecting step.
2. The method of claim 1, further comprising: adjusting a torque
conversion characteristic of the torque regulator to reduce a
mechanical torque applied to a shaft of the synchronous generator,
wherein the adjusting a torque conversion characteristic step is
initiated in response to the detecting step.
3. The method of claim 1, wherein the torque regulator comprises a
torque-regulating gearbox, that in turn comprises a hydraulic
circuit, the method further comprising: reducing a mass flow of
hydraulic fluid through the hydraulic circuit, wherein the reducing
a mass flow step is initiated in response to the detecting
step.
4. The method of claim 1, wherein the torque regulator comprises a
torque-regulating gearbox, that in turn comprises a plurality of
guide vanes disposed in a guide vanes housing, the method further
comprising: adjusting a position of the plurality of guide vanes,
wherein the adjusting a position step is initiated in response to
the detecting step.
5. The method of claim 1, wherein the torque regulator comprises a
torque-regulating gearbox (TRG), the method further comprising:
adjusting an amount of energy absorbed by the TRG, wherein the
adjusting an amount of energy step is initiated in response to the
detecting step.
6. The method of claim 1, further comprising: applying a brake
disposed in a drive train between the turbine rotor and the torque
regulator to reduce a rotational speed of the turbine rotor,
wherein the applying a brake step is initiated in response to the
detecting step.
7. The method of claim 6, wherein the applying a brake step is
controlled dependent upon a characteristic of a voltage of the
power grid.
8. The method of claim 6, wherein the applying a brake step is
controlled to be proportional to a voltage of the power grid.
9. The method of claim 1, further comprising: adjusting a blade
pitch of a plurality of blades of the wind turbine to reduce a
rotational speed of the turbine rotor, wherein the adjusting a
blade pitch step is initiated in response to the detecting
step.
10. The method of claim 1, further comprising: isolating one or
more electrical peripherals associated with the wind turbine from
the power grid during the low voltage event, wherein the isolating
step is initiated in response to the detecting step.
11. The method of claim 1, further comprising: providing an
uninterruptable power supply (UPS) operative to provide power to
one or more components of the wind turbine during the low voltage
event.
12. The method of claim 11, wherein the UPS is selected from the
group consisting of at least one battery power supply, a
photovoltaic cell, a capacitor, a flywheel, and any combination
thereof.
13. The method of claim 1, wherein the synchronous generator is
configured to have a relatively high dynamic pull-out torque.
14. The method of claim 1, wherein the synchronous generator is
configured to have a d-axis synchronous reactance of less than
about 1.4 p.u.
15. The method of claim 1, wherein the synchronous generator is
configured to have a relatively low sub-transient reactance and
relatively low d-axis open circuit transient time constant.
16. The method of claim 1, wherein the synchronous generator is
configured to have a sub-transient reactance of less than about
0.15 p.u. and a d-axis open circuit transient time constant of less
than about 3 p.u.
17. The method of claim 1, further comprising: determining that a
voltage of the power grid has returned to a predetermined level
following the low voltage event; and resuming normal operation of
the wind turbine.
18. A wind turbine that may remain electrically connected to a
power grid during a low voltage event, the wind turbine comprising:
a synchronous generator; a torque regulator coupled to the
synchronous generator; a turbine rotor coupled to the torque
regulator and comprising a plurality of turbine blades; and a
controller operative to detect an occurrence of a low voltage event
and, in response to detecting the low voltage event, to cause a
boost in a rotor current of the synchronous generator to provide
reactive power to the power arid during the low voltage event.
19. The wind turbine of claim 18, wherein the torque regulator
comprises a torque-regulating gearbox (TRG), that in turn comprises
a plurality of guide vanes operative to modify a torque conversion
between the turbine rotor and the synchronous generator, and
wherein the controller is operative to adjust a position of the
plurality of guide vanes in response to the low voltage event to
reduce a mechanical torque applied to the synchronous
generator.
20. The wind turbine of claim 19, wherein the TRG comprises a
hydraulic circuit, and wherein the plurality of guide vanes are
disposed in the hydraulic circuit.
21. The wind turbine of claim 18, wherein the torque regulator
comprises a torque-regulating gearbox (TRG), and wherein the
controller is operative to adjust an amount of energy absorbed by
the TRG.
22. The wind turbine claim 18, further comprising: a brake
associated with a drive train extending between the turbine rotor
and the torque regulator, wherein the controller is operative to
apply the brake in response to the low voltage event to reduce a
rotational speed of the turbine rotor.
23. The wind turbine of claim 22, wherein the controller is
operative to selectively apply the brake dependent upon a
characteristic of a voltage of the power grid.
24. The wind turbine of claim 22, wherein the controller is
operative to selectively apply the brake dependent upon and
proportional to a dip in a voltage of the power grid.
25. The wind turbine of claim 18, wherein the controller is further
operative to adjust a blade pitch of the plurality of turbine
blades in response to the low voltage event to reduce a rotational
speed of the turbine rotor.
26. The wind turbine of claim 18, further comprising: one or more
electrical peripherals selected from the group consisting of a yaw
drive, a hydraulic pump, and an electric motor; wherein the
controller is further operative to isolate the one or more
electrical peripherals from the power grid during the low voltage
event.
27. The wind turbine of claim 18, further comprising: an
uninterruptable power supply (UPS) operative to provide power to
one or more components of the wind turbine during the low voltage
event.
28. The wind turbine of claim 27, wherein the UPS is selected from
the group consisting of at least one battery power supply, a
photovoltaic cell, a capacitor, a flywheel, and any combination
thereof.
29. The wind turbine of claim 18, wherein the synchronous generator
is configured to have a relatively high dynamic pull-out
torque.
30. The wind turbine of claim 18, wherein the synchronous generator
is configured to have a d-axis synchronous reactance of less than
about 1.4 p.u.
31. The wind turbine of claim 18, wherein the synchronous generator
is configured to have a relatively low sub-transient reactance and
relatively low d-axis open circuit transient time constant.
32. The wind turbine of claim 18, wherein the synchronous generator
is configured to have a sub-transient reactance of less than about
0.15 p.u. and a d-axis open circuit transient time constant of less
than about 3 p.u.
33. The wind turbine of claim 18, wherein the controller is further
operative to determine that a voltage of the power grid has
returned to a predetermined level following the low voltage event,
and to resume normal operation of the wind turbine.
34. An automated method for allowing a wind turbine to remain
electrically connected to a power grid during a low voltage event,
the wind turbine comprising a synchronous generator coupled to the
power grid and to a turbine rotor through a torque regulator, the
method comprising: detecting a low voltage event; boosting a rotor
current of the synchronous generator in response to the detecting
step and to provide reactive power to the power grid during the low
voltage event; adjusting a torque conversion characteristic of the
torque regulator in response to the detecting step and to reduce a
mechanical torque applied to a shaft of the synchronous generator;
adjusting a blade pitch of a plurality of blades of the wind
turbine in response to the detecting step and to reduce a
rotational speed of the turbine rotor; applying a brake disposed
between the turbine rotor and the torque regulator in response to
the detecting step and to reduce a rotational speed of the turbine
rotor; isolating one or more electrical peripherals associated with
the wind turbine from the power grid in response to the detecting
step; providing an uninterruptable power supply (UPS) operative to
provide power to one or more components of the wind turbine during
the low voltage event; determining that a voltage of the power grid
has returned to a predetermined level following the low voltage
event; and resuming normal operation of the wind turbine.
35. The method of claim 34, wherein the torque regulator comprises
a torque-regulating gearbox, that in turn comprises a hydraulic
circuit, and wherein the adjusting a torque conversion
characteristic step comprises: reducing a mass flow of hydraulic
fluid through the hydraulic circuit.
36. The method of claim 34, wherein the torque regulator comprises
a torque-regulating gearbox, that in turn comprises a plurality of
guide vanes disposed in a guide vanes housing, and wherein the
adjusting a torque conversion characteristic step comprises:
adjusting a position of the plurality of guide vanes.
37. The method of claim 34, wherein the torque regulator comprises
a regulating gearbox (TRG), and wherein the adjusting a torque
conversion characteristic step comprises: adjusting an amount of
energy absorbed by the TRG.
38. The method of claim 34, wherein the applying a brake step is
controlled dependent upon a characteristic of a voltage of the
power grid.
39. The method of claim 34, wherein the applying a brake step is
controlled to be proportional to a voltage of the power grid.
40. The method of claim 34, wherein the UPS is selected from the
group consisting of at least one battery power supply, a
photovoltaic cell, a capacitor, a flywheel, and any combination
thereof.
41. The method of claim 34, wherein the synchronous generator is
configured to have a relatively high dynamic pull-out torque.
42. The method of claim 34, wherein the synchronous generator is
configured to have a d-axis synchronous reactance of less than
about 1.4 p.u.
43. The method of claim 34, wherein the synchronous generator is
configured to have a relatively low sub-transient reactance and
relatively low d-axis open circuit transient time constant.
44. The method of claim 34, wherein the synchronous generator is
configured to have a sub-transient reactance of less than about
0.15 p.u. and a d-axis open circuit transient time constant of less
than about 3 p.u.
45. An automated method for allowing a wind turbine to remain
electrically connected to a power grid during a low voltage event,
the wind turbine comprising a synchronous generator coupled to the
power grid and to a turbine rotor through a torque regulator, the
method comprising: detecting a low voltage event; initiating a
first action in response to the detecting step, wherein the first
action comprises executing at least one step selected from the
group consisting of: a) boosting a rotor current of the synchronous
generator to provide reactive power to the power grid during the
low voltage event; and b) adjusting a torque conversion
characteristic of the torque regulator to reduce a mechanical
torque applied to a shaft of the synchronous generator; and
initiating a second action in response to the detecting step,
wherein the second action comprises executing at least one step
selected from the group consisting of: a) applying a brake disposed
in a drive train between the turbine rotor and the torque regulator
to reduce a rotational speed of the turbine rotor; and b) adjusting
a blade pitch of a plurality of blades of the wind turbine to
reduce a rotational speed of the turbine rotor.
46. An automated method for allowing a wind turbine to remain
electrically connected to a power grid during a low voltage event,
the wind turbine comprising a synchronous generator coupled to the
power grid and to a turbine rotor through a torque regulator, the
method comprising: detecting a low voltage event; and adjusting
operation of the torque regulator, wherein the adjusting operation
step is initiated in response to the detecting step.
47. The method of claim 46, wherein the adjusting operation step
comprises adjusting a torque conversion characteristic of the
torque regulator.
48. The method of claim 46, wherein the adjusting operation step
comprises reducing a mechanical torque applied to a shaft of the
synchronous generator.
49. The method of claim 46, wherein the torque regulator comprises
a torque-regulating gearbox, that in turn comprises a hydraulic
circuit, and wherein the adjusting operation step comprises:
reducing a mass flow of hydraulic fluid through the hydraulic
circuit.
50. The method of claim 46, wherein the torque regulator comprises
a torque-regulating gearbox, that in turn comprises a plurality of
guide vanes disposed in a guide vanes housing, and wherein the
adjusting operation step comprises: adjusting a position of the
plurality of guide vanes.
51. The method of claim 46, wherein the torque regulator comprises
a torque-regulating gearbox (TRG), and wherein the adjusting
operation step comprises: adjusting an amount of energy absorbed by
the TRG.
52. The method of any of claims 16 51 claim 46, further comprising:
applying a brake disposed in a drive train between the turbine
rotor and the torque regulator to reduce a rotational speed of the
turbine rotor, wherein the applying a brake step is initiated in
response to the detecting step.
53. The method of claim 52, wherein the applying a brake step is
controlled dependent upon a characteristic of a voltage of the
power grid.
54. The method of claim 52, wherein the applying a brake step is
controlled to be proportional to a voltage of the power grid.
55. The method of claim 46, further comprising: adjusting a blade
pitch of a plurality of blades of the wind turbine to reduce a
rotational speed of the turbine rotor, wherein the adjusting a
blade pitch step is initiated in response to the detecting
step.
56. The method of claim 46, further comprising: isolating one or
more electrical peripherals associated with the wind turbine from
the power grid during the low voltage event.
57. The method of claim 46, further comprising: providing an
uninterruptable power supply (UPS) operative to provide power to
one or more components of the wind turbine during the low voltage
event.
58. The method of claim 57, wherein the UPS is selected from the
group consisting of at least one of battery power supply a
photovoltaic cell, a capacitor, a flywheel, and any combination
thereof.
59. The method of claim 46, wherein the synchronous generator is
configured to have a relatively high dynamic pull-out torque.
60. The method of claim 46, wherein the synchronous generator is
configured to have a d-axis synchronous reactance of less than
about 1.4 p.u.
61. The method of claim 46, wherein the synchronous generator is
configured to have a relatively low sub-transient reactance and
relatively low d-axis open circuit transient time constant.
62. The method of claim 46, wherein the synchronous generator is
configured to have a sub-transient reactance of less than about
0.15 p.u. and a d-axis open circuit transient time constant of less
than about 3 p.u.
63. The method of claim 46, further comprising: boosting a rotor
current of the synchronous generator to provide reactive power to
the power grid during the low voltage event, wherein the boosting
step is initiated in response to the detecting step.
64. The method of claim 46, further comprising: determining that a
voltage of the power grid has returned to a predetermined level
following the low voltage event; and resuming normal operation of
the wind turbine.
65. A wind turbine that may remain electrically connected to a
power grid during a low voltage event. the wind turbine comprising:
a synchronous generator; a torque regulator coupled to the
synchronous generator; a turbine rotor coupled to the torque
regulator and comprising a plurality of turbine blades; and a
controller operative to detect an occurrence of a low voltage event
and, in response to detecting the low voltage event, to adjust
operation of the torque regulator.
66. The wind turbine of claim 65, wherein the torque regulator
comprises a torque regulating gearbox (TRG), that in turn comprises
a plurality of guide vanes operative to modify a torque conversion
between the turbine rotor and the synchronous generator, and
wherein the controller is operative to adjust a position of the
plurality of guide vanes in response to the low voltage event to
reduce a mechanical torque applied to the synchronous
generator.
67. The wind turbine of claim 66, wherein the TRG comprises a
hydraulic circuit, and wherein the plurality of guide vanes are
disposed in the hydraulic circuit.
68. The wind turbine of claim 65, wherein the torque regulator
comprises a variable speed torque-regulating gearbox (TRG), wherein
the controller is operative to adjust an amount of energy absorbed
by the TRG.
69. The wind turbine claim 65, further comprising: a brake disposed
in a drive train between the turbine rotor and the torque
regulator, wherein the controller is operative to apply the brake
in response to the low voltage event to reduce a rotational speed
of the turbine rotor.
70. The wind turbine of claim 69, wherein the controller is
operative to selectively apply the brake dependent upon a
characteristic of a voltage of the power grid.
71. The wind turbine of claim 69, wherein the controller is
operative to selectively apply the brake dependent upon and
proportional to a voltage of the power grid.
72. The wind turbine of claim 65, wherein the controller is further
operative to adjust a blade pitch of the plurality of turbine
blades in response to the low voltage event to reduce a rotational
speed of the turbine rotor.
73. The wind turbine of claim 65, further comprising: one or more
electrical peripherals selected from the group consisting of a yaw
drive, a hydraulic pump, and an electric motor; wherein the
controller is further operative to isolate the one or more
electrical peripherals from the power grid during the low voltage
event.
74. The wind turbine of claim 65, further comprising: an
uninterruptable power supply (UPS) operative to provide power to
one or more components of the wind turbine during the low voltage
event.
75. The wind turbine of claim 74, wherein the UPS is selected from
the group consisting of at least one battery power supply, a
photovoltaic cell, a capacitor, a flywheel, and any combination
thereof.
76. The wind turbine of claim 65, wherein the synchronous generator
is configured to have a relatively high dynamic pull-out
torque.
77. The wind turbine of claim 65, wherein the synchronous generator
is configured to have a d-axis synchronous reactance of less than
about 1.4 p.u.
78. The wind turbine of claim 65, wherein the synchronous generator
is configured to have a relatively low sub-transient reactance and
relatively low d-axis open circuit transient time constant.
79. The wind turbine of claim 65, wherein the synchronous generator
is configured to have a sub-transient reactance of less than about
0.15 p.u. and a d-axis open circuit transient time constant of less
than about 3 p.u.
80. The wind turbine of claim 65, wherein the controller is
operative to cause a boost in a rotor current of the synchronous
generator to provide reactive power to the power grid during the
low voltage event.
81. The wind turbine of claim 65, wherein the controller is further
operative to determine that a voltage of the power grid has
returned to a predetermined level following the low voltage event,
and to resume normal operation of the wind turbine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority under 35 U.S.C.
.sctn.119(e) to pending U.S. Provisional Patent Application Ser.
No. 61/148,777, that is entitled "LOW VOLTAGE RIDE THROUGH FOR WIND
TURBINES," that was filed on Jan. 30, 2009, and the entire
disclosure of which is hereby incorporated by reference in its
entirety herein.
FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of wind
turbines and, more particularly, to configuring/operating a wind
turbine to remain connected to a power grid during a low voltage
ride through condition.
BACKGROUND
[0003] The application of wind-powered generating systems in the
past has been on a small scale when compared to the total
generating capacity of an electrical power grid. A term that is
often used to describe the relative quantity of wind-generated
power is "penetration." Penetration is the ratio of wind-generated
power to the total available generated power for a power grid.
Previously, even in those locations where wind-generated power is
the highest, the penetration levels were in the range of a few
percent. While this is a relatively small amount of power, and the
rules that govern the operation of the wind turbines reflect this
small penetration, it is clear that the penetration is increasing
and therefore the operating rules for the wind turbines are and
will be changing. For example, one operating principle that is
being revised is the required amount of grid stability support that
must be provided by wind turbines. As can be appreciated, as the
penetration of wind turbines increases, the expectation that they
contribute to the stability of powers grids becomes greater.
[0004] Power utilities today face an ever-growing demand for higher
quality, reliable power and increased transmission capacity. A key
to increasing reliability and capacity is ensuring that grid
voltage is properly regulated. This helps prevent service
disruptions, damage to electrical service equipment, generating
plants, and other components of the power grid and can help
maximize transmission capacity. In order to reliably supply power
to the power grid, wind turbine generators (as well as other types
of generators) must conform to power grid interconnection standards
that define requirements imposed on power suppliers and large power
consumers. One such standard is a "low voltage ride through" (LVRT)
requirement which typically requires that a power generation unit
remain connected and synchronized to the power grid when the
voltage at the terminals of the generation unit fall to prescribed
levels for prescribed periods of time (e.g., 15% of rated level for
0.5 seconds, or the like).
[0005] The LVRT requirement has been addressed in steam and gas
turbine generator plants through use of vital electrical buses that
are powered by DC power sources and by auxiliary buses connected to
the generators. Since the input power (i.e., steam or gas) can be
closely regulated, these types of generators are typically more
resistant to voltage fluctuations than are wind turbine generators,
which are dependent upon highly variable wind speeds to supply the
mechanical energy. In the past, wind turbine generators have been
allowed to trip offline during a low voltage event to protect them
from harm. However, for reasons noted above, it is becoming more
important that the wind turbines include LVRT capabilities to
support the power grid during these undesirable voltage
fluctuations.
SUMMARY
[0006] The present invention at least generally relates to
configuring and/or operating a wind turbine to remain connected to
a power grid during a low voltage ride through condition. The
present invention may be utilized by a wind turbine that is being
operated as a stand-alone unit, but also may be utilized by one or
more wind turbines within a wind farm/park (e.g., where a plurality
of wind turbines are interconnected or at least may be
interconnected with a power grid through a point of common
coupling). Regardless of its manner of implementation, a wind
turbine according to the present invention may include a turbine
rotor (e.g., with one or more associated blades), a synchronous
generator, a torque regulator or "TR" in a drive train between the
turbine rotor and synchronous generator (e.g., one such TR being a
torque-regulating gearbox (TRG)), and possibly other components.
Embodiments of the invention may include configuring and operating
the above-noted and other components to facilitate fault voltage
ride through functionality (e.g., low voltage ride through
functionality) for the wind turbine. Various aspects of the present
invention will now be described. Although each of the following
aspects may relate or be applicable to the foregoing, the content
of this introduction is not a requirement for any of these aspects
unless otherwise noted.
[0007] A first aspect of the present invention is embodied by an
automated method that allows a wind turbine to remain electrically
connected with a power grid during a low voltage event. The wind
turbine may include a synchronous generator coupled to the power
grid and to a turbine rotor through a torque regulator (e.g., a
TRG). The automated method may include detecting a low voltage
event. Further, the automated method may include boosting a rotor
current of the synchronous generator to provide reactive power to
the power grid during the low voltage event, wherein the boosting
of rotor current is initiated in response to detecting the low
voltage event.
[0008] A number of feature refinements and additional features are
applicable to the first aspect of the present invention. These
feature refinements and additional features may be used
individually or in any combination. The following discussion is
separately applicable to the first aspect, up to the start of the
discussion of a second aspect of the present invention.
[0009] In an embodiment of the first aspect, the automated method
may include adjusting operation of the torque regulator, for
instance to change the amount of torque that is transferred between
the turbine rotor and the synchronous generator (e.g., to reduce
the torque applied to a shaft of the synchronous generator in
response to the detection of the low voltage event). The torque
regulator may be of any appropriate size, shape, configuration,
and/or type. Any appropriate way of regulating the torque transfer
from the turbine rotor to the synchronous generator may be utilized
(e.g., electrically, hydraulically).
[0010] In an embodiment of the first aspect, the automated method
may include adjusting a torque conversion characteristic of a
torque regulator in the form of a TRG (e.g., to reduce a mechanical
torque applied to a shaft of the synchronous generator), wherein
the adjustment of the torque conversion characteristic is initiated
in response to the detection of the low voltage event. The TRG may
include a hydraulic circuit, and the automated method may include
reducing a mass flow of hydraulic fluid through the hydraulic
circuit (e.g., to modify the operational characteristics of the
TRG), wherein the reduction of mass flow is initiated in response
to the detection of the low voltage event. Further, the TRG may
include a plurality of guide vanes disposed in a guide vane
housing, and the automated method may include adjusting a position
of the guide vanes to, for example, modify the mass flow of
hydraulic fluid through the hydraulic circuit, wherein the guide
vane adjustment is initiated in response to the detection of the
low voltage event. The automated method of the first aspect may
also include adjusting an amount of energy absorbed by the TRG in
response to the detection of the low voltage event, which may be
advantageous for maintaining the electrical connection between the
wind turbine and the power grid during the low voltage event.
[0011] In an embodiment of the first aspect, the automated method
may include initiating a reduction in a rotational speed of the
turbine rotor (e.g., in response to the detection of the low
voltage event). The rotational speed of the turbine rotor may be
reduced in any appropriate manner (e.g., activating or applying one
or more brakes or braking devices of any appropriate type, changing
the pitch of the turbine rotor blades, or both). The amount that
the rotational speed of the turbine rotor is reduced may be
undertaken on any appropriate basis.
[0012] In an embodiment of the first aspect, the automated method
may include activating or applying at least one brake associated
with a drive train that extends between the turbine rotor and the
synchronous generator (e.g., to reduce a rotational speed of the
turbine rotor), wherein such braking may be initiated in response
to the detection of the low voltage event. As an example, the
braking may be controlled so to be dependent upon and/or
proportional to a voltage of the power grid (or on any other
appropriate basis).
[0013] The automated method of the first aspect of the present
invention may also include adjusting a blade pitch of a plurality
of blades of the wind turbine in response to the detection of the
low voltage event (e.g., to reduce a rotational speed of the
turbine rotor). The automated method may also include isolating one
or more electrical peripherals associated with the wind turbine
from the power grid during the low voltage event, wherein this
isolation is initiated in response to the detection of the low
voltage event. In this regard, the potential harm caused by the low
voltage event to the one or more electrical peripherals may be
significantly reduced. The automated method may further include
providing an uninterruptable power supply (UPS) operative to
provide power to one or more components of the wind turbine during
the low voltage event. As an example, the UPS may include a battery
power supply, although one or more energy storage devices of any
appropriate type may be utilized.
[0014] A second aspect of the present invention is embodied by a
wind turbine that may remain electrically connected to a power grid
during a low voltage event. The wind turbine may include a turbine
rotor, a torque regulator (e.g., a TRG), and a synchronous
generator, where the turbine rotor includes a plurality of turbine
blades, and where the torque regulator is located between the
turbine rotor and the synchronous generator (e.g., such that the
synchronous generator is coupled to the turbine rotor through the
torque regulator; such that the torque regulator is in a drive
train that extends between the turbine rotor and the synchronous
generator). Further, the wind turbine may include a controller that
is operative to detect an occurrence of a low voltage event and, in
response to detecting such a low voltage event, to cause a boost in
a rotor current of the synchronous generator to provide reactive
power to the power grid during the low voltage event.
[0015] A number of feature refinements and additional features are
applicable to the second aspect of the present invention. These
feature refinements and additional features may be used
individually or in any combination. The following discussion is
separately applicable to the second aspect, up to the start of the
discussion of a third aspect of the present invention.
[0016] The torque regulator may be of any appropriate size, shape,
configuration, and/or type. Any appropriate way of regulating the
torque transfer from the turbine rotor to the synchronous generator
may be utilized (e.g., electrically, hydraulically). In an
embodiment of the second aspect where the torque regulator is in
the form of a TRG, the TRG of the wind turbine may include a
plurality of guide vanes operative to modify a torque conversion
between the turbine rotor and the synchronous generator. Further,
the controller may be operative to adjust a position of the
plurality of guide vanes in response to the low voltage event to
reduce a mechanical torque applied to the synchronous generator.
For example, the TRG may include a hydraulic circuit, and the
plurality of guide vanes may be disposed in the hydraulic circuit.
In an embodiment of the second aspect, the controller may be
operative to adjust an amount of energy absorbed by the TRG, which
may be advantageous for maintaining the electrical connection
between the wind turbine and the power grid during the low voltage
event.
[0017] One or more brakes or braking devices of any appropriate
type may be incorporated in any appropriate manner in a drive train
that extends between the turbine rotor and synchronous generator
(e.g., to reduce the rotational speed of the turbine rotor on any
appropriate basis). In an embodiment of the second aspect, the wind
turbine may include a brake associated with a shaft disposed
between the turbine rotor and the torque regulator. In any case,
the controller may be operative to activate or apply at least one
brake in response to the detection of the low voltage event (e.g.,
to reduce a rotational speed of the turbine rotor). As an example,
the controller may be operative to selectively activate or apply at
least one brake dependent upon and/or proportional to a voltage of
the power grid (or on any other appropriate basis).
[0018] The controller of the wind turbine of the second aspect of
the present invention may also be operative to adjust a blade pitch
of the plurality of blades of the wind turbine in response to the
low voltage event (e.g., to reduce a rotational speed of the
turbine rotor). The wind turbine may also include one or more
electrical peripherals (e.g., a yaw drive, a hydraulic pump, an
electric motor, or the like) associated with the wind turbine, and
the controller may be operative to isolate the One or more
electrical peripherals from the power grid during the low voltage
event. In this regard, the potential harm caused by the low voltage
event to the one or more electrical peripherals may be
significantly reduced. The wind turbine may further include an
uninterruptable power supply (UPS) operative to provide power to
one or more components of the wind turbine during the low voltage
event. As an example, the UPS may include a battery power supply,
although one or more energy storage devices of any appropriate type
may be utilized. Further, the controller may be further operative
to determine that a voltage of the power grid has returned to a
predetermined level following the low voltage event, and to resume
normal operation of the wind turbine.
[0019] A third aspect of the present invention is embodied by an
automated method that allows a wind turbine to remain electrically
connected with a power grid during a low voltage event. The wind
turbine may include a synchronous generator coupled to the power
grid and to a turbine rotor through a torque regulator (e.g., a
TRG). The automated method may include detecting a low voltage
event, and in response: 1) boosting a rotor current of the
synchronous generator (e.g., to provide reactive power to the power
grid during the low voltage event); 2) adjusting a torque
conversion characteristic of the torque regulator (e.g., to reduce
a mechanical torque applied to a shaft of the synchronous
generator); 3) adjusting a blade pitch of a plurality of blades of
the wind turbine (e.g., to reduce a rotational speed of the turbine
rotor); 4) activating or applying at least one brake associated
with a drive train that extends disposed between the turbine rotor
and the synchronous generator (e.g., to reduce a rotational speed
of the turbine rotor); 5) isolating one or more electrical
peripherals associated with the wind turbine from the power grid;
and 6) providing an uninterruptable power supply (UPS) (e.g., a
battery power supply, or more generally one or more energy storage
devices of any appropriate type) operative to provide power to one
or more components of the wind turbine during the low voltage
event. Additionally, the automated method may include determining
that a voltage of the power grid has returned to a predetermined
level following the low voltage event, and resuming normal
operation of the wind turbine.
[0020] A number of feature refinements and additional features are
applicable to the third aspect of the present invention. These
feature refinements and additional features may be used
individually or in any combination. The following discussion is
separately applicable to the third aspect, up to the start of the
discussion of a fourth aspect of the present invention.
[0021] In an embodiment of the third aspect, the torque regulator
is in the form of a TRG. The TRG may include a hydraulic circuit,
and the adjustment of a torque conversion characteristic may
include reducing a mass flow of hydraulic fluid through the
hydraulic circuit to modify the operational characteristics of the
TRG. Further, the TRG may include a plurality of guide vanes
disposed in a guide vane housing, and the adjustment of a torque
conversion characteristic may include adjusting a position of the
guide vanes to, for example, modify the mass flow of hydraulic
fluid through the hydraulic circuit. In an embodiment of the third
aspect, the adjustment of a torque conversion characteristic may
also include adjusting an amount of energy absorbed by the TRG,
which may be advantageous for maintaining the electrical connection
between the wind turbine and the power grid during the low voltage
event.
[0022] A fourth aspect of the present invention is embodied by an
automated method that allows a wind turbine to remain electrically
connected with a power grid during a low voltage event. The wind
turbine associated with this embodiment may include a synchronous
generator coupled to the power grid and to a turbine rotor through
a torque regulator (e.g., a torque-regulating gearbox (TRG)). The
automated method may include detecting a low voltage event. The
automated method may also include initiating a first action in
response to the detection of a low voltage event, wherein the first
action includes executing at least one step selected from the group
consisting of: a) boosting a rotor current of the synchronous
generator (e.g., to provide reactive power to the power grid during
the low voltage event); and b) adjusting a torque conversion
characteristic of the torque regulator (e.g., to reduce a
mechanical torque applied to a shaft of the synchronous generator).
The automated method may also include initiating a second action in
response to the detection of a low voltage event, wherein the
second action includes executing at least one step selected from
the group consisting of: a) activating or applying at least one
brake associated with a drive train that extends between the
turbine rotor and the synchronous generator (e.g., to reduce a
rotational speed of the turbine rotor); and b) adjusting a blade
pitch of a plurality of blades of the wind turbine (e.g., to reduce
a rotational speed of the turbine rotor).
[0023] A fifth aspect of the present invention is embodied by an
automated method that allows a wind turbine to remain electrically
connected with a power grid during a low voltage event. The wind
turbine associated with this embodiment may include a synchronous
generator coupled to the power grid and to a turbine rotor through
a torque regulator (e.g., a torque-regulating gearbox (TRG)). The
automated method may include detecting a low voltage event. The
automated method may also include adjusting operation of the torque
regulator, wherein the operational adjustment is initiated in
response to the detection of the low voltage event.
[0024] A number of feature refinements and additional features are
applicable to the fifth aspect of the present invention. These
feature refinements and additional features may be used
individually or in any combination. The following discussion is
separately applicable to the fifth aspect, up to the start of the
discussion of a sixth aspect of the present invention.
[0025] In an embodiment of the fifth aspect, the operational
adjustment includes adjusting a torque conversion characteristic of
the torque regulator. For example, the operational adjustment may
include reducing a mechanical torque applied to a shaft of the
synchronous generator. Additionally, in an embodiment of the fifth
aspect where the torque regulator is in the form of a TRG, the TRG
may include a hydraulic circuit, and the operational adjustment may
include reducing a mass flow of hydraulic fluid through the
hydraulic circuit to modify the operational characteristics of the
TRG. Further, the TRG may include a plurality of guide vanes
disposed in a guide vane housing, and the operational adjustment
may include adjusting a position of the guide vanes to, for
example, modify a mass flow of hydraulic fluid through the
hydraulic circuit. In an embodiment of the fifth aspect, the
automated method may also include adjusting an amount of energy
absorbed by the TRG, which may be advantageous for maintaining the
electrical connection between the wind turbine and the power grid
during the low voltage event.
[0026] In an embodiment of the fifth aspect, the automated method
may include activating or applying at least one brake associated
with a drive train that extends between the turbine rotor and the
synchronous generator (e.g., to reduce a rotational speed of the
turbine rotor) in response to the detection of the low voltage
event. As an example, the braking may be controlled so as to be
dependent upon and/or proportional to a voltage of the power grid
(or on any other appropriate basis). Further, the automated method
may include boosting a rotor current of the synchronous generator
to provide reactive power to the power grid during the low voltage
event, wherein the boosting of rotor current is initiated in
response to detecting the low voltage event.
[0027] The automated method of the fifth aspect of the present
invention may also include adjusting a blade pitch of a plurality
of blades of the wind turbine in response to the detection of the
low voltage event (e.g., to reduce a rotational speed of the
turbine rotor). The automated method may also include isolating one
or more electrical peripherals associated with the wind turbine
from the power grid during the low voltage event. In this regard,
the potential harm caused by the low voltage event to the one or
more electrical peripherals may be significantly reduced. The
automated method may further include providing an uninterruptable
power supply (UPS) operative to provide power to one or more
components of the wind turbine during the low voltage event. As an
example, the UPS may include a battery power supply, although one
or more energy storage devices of any appropriate type may be
utilized.
[0028] A sixth aspect of the present invention is embodied by a
wind turbine that may remain electrically connected to a power grid
during a low voltage event. The wind turbine may include a
synchronous generator and a torque regulator coupled to the
synchronous generator. The wind turbine may also include a turbine
rotor coupled to the torque regulator, where the turbine rotor
includes a plurality of turbine blades. Further, the wind turbine
may include a controller that is operative to detect an occurrence
of a low voltage event and, in response to detecting the low
voltage event, to adjust operation of the torque regulator.
[0029] A number of feature refinements and additional features are
applicable to the sixth aspect of the present invention. These
feature refinements and additional features may be used
individually or in any combination.
[0030] In an embodiment of the sixth aspect where the torque
regulator is in the form of a TRG, the TRG of the wind turbine may
include a plurality of guide vanes operative to modify a torque
conversion between the turbine rotor and the synchronous generator.
Further, the controller may be operative to adjust a position of
the plurality of guide vanes in response to the low voltage event
(e.g., to reduce a mechanical torque applied to the synchronous
generator). For example, the TRG may include a hydraulic circuit,
and the plurality of guide vanes may be disposed in the hydraulic
circuit. In an embodiment of the second aspect, the controller may
be operative to adjust an amount of energy absorbed by the TRG,
which may be advantageous for maintaining the electrical connection
between the wind turbine and the power grid during the low voltage
event.
[0031] In an embodiment of the sixth aspect, the wind turbine may
include at least one brake associated with a drive train that
extends between the turbine rotor and the synchronous generator.
Further, the controller may be operative to activate or apply at
least one brake in response to the low voltage event (e.g., to
reduce a rotational speed of the turbine rotor). As an example, the
controller may be operative to selectively activate or apply the at
least one brake dependent upon and/or proportional to a voltage of
the power grid (or on any other appropriate basis). Further, the
controller may be operative to cause a boost in a rotor current of
the synchronous generator to provide reactive power to the power
grid during the low voltage event.
[0032] The controller of the wind turbine of the sixth aspect of
the present invention may also be operative to adjust a blade pitch
of the plurality of blades of the wind turbine in response to the
low voltage event (e.g., to reduce a rotational speed of the
turbine rotor). The wind turbine may also include one or more
electrical peripherals (e.g., a yaw drive, a hydraulic pump, an
electric motor, or the like) associated with the wind turbine, and
the controller may be operative to isolate the one or more
electrical peripherals from the power grid during the low voltage
event. In this regard, the potential harm caused by the low voltage
event to the one or more electrical peripherals may be
significantly reduced. The wind turbine may further include an
uninterruptable power supply (UPS) operative to provide power to
one or more components of the wind turbine during the low voltage
event. As an example, the UPS may include a battery power supply,
although one or more energy storage devices of any appropriate type
may be utilized. Further, the controller may be further operative
to determine that a voltage of the power grid has returned to a
predetermined level following the low voltage event, and to resume
normal operation of the wind turbine.
[0033] A number of feature refinements and additional features are
separately applicable to each of above-noted aspects of the present
invention. These feature refinements and additional features may be
used individually or in any combination in relation to each of the
above-noted aspects of the present invention. Any feature of any
other various aspects of the present invention that is intended to
be limited to a "singular" context or the like will be clearly set
forth herein by terms such as "only," "single," "limited to," or
the like. Merely introducing a feature in accordance with commonly
accepted antecedent basis practice does not limit the corresponding
feature to the singular (e.g., indicating that a wind turbine
includes "a brake" alone does not mean that the wind turbine
includes only a single brake). Moreover, any failure to use phrases
such as "at least one" also does not limit the corresponding
feature to the singular (e.g., indicating that a wind turbine
includes "a brake" alone does not mean that the wind turbine
includes only a single brake). Finally, use of the phrase "at least
generally" or the like in relation to a particular feature
encompasses the corresponding characteristic and insubstantial
variations thereof (e.g., indicating that a part is at least
generally cylindrical encompasses the part being cylindrical).
[0034] Any torque regulator or the torque-regulating function
addressed in relation to the present invention may utilize one or
more torque-regulating devices or a torque-regulating system of any
appropriate size, shape, configuration, and/or type. Torque may be
regulated or adjusted (e.g., to reduce the torque transmitted to a
shaft of the synchronous generator) in any appropriate manner
(e.g., electrically, hydraulically). In one embodiment, the torque
regulator is in the form of a TRG. Such a TRG may include a
combination of a hydraulic or hydrodynamic torque converter and a
planetary gear system (e.g., a multi-stage, functionally
interconnected revolving planetary gear system).
[0035] Any brake or braking function addressed in relation to the
present invention, for purposes of reducing a rotational speed of
the turbine rotor in response to a low voltage event, may utilize
one or more brakes or braking devices (more generally, a braking
system) of any appropriate size, shape, configuration, and/or type.
Each such brake may be implemented in any appropriate manner in
relation to a drive train that extends from the turbine rotor to
the synchronous generator, for instance so as to be disposed
between the turbine rotor and the torque regulator.
[0036] Unless otherwise noted herein, each of the various actions
addressed herein and that may be initiated in response to the
detection of a low voltage event may be initiated in any
appropriate order, including where one or more actions are
initiated sequentially, where one or more actions are initiated
simultaneously, or any combination thereof. Moreover, once a
determination has been made that the low voltage event has
concluded (e.g., that a voltage of the power grid has returned to a
predetermined level), normal operation of the wind turbine may be
resumed.
[0037] The synchronous generator addressed herein may be configured
to have a relatively low d-axis synchronous reactance (e.g., less
than about 1.4 p.u.). As an example, the synchronous generator may
be configured to have a relatively low sub-transient reactance
(e.g., less than about 0.15 p.u.), and a relatively low d-axis open
circuit transient time constant (e.g., less than about 3 p.u.). As
can be appreciated, the term "p.u." refers to "per-unit," which is
a commonly used system for describing various characteristics
(e.g., power, voltage, current, and impedance) of power systems and
components of power systems using normalized values.
[0038] In addition to the exemplary aspects and embodiments
described above, further aspects and embodiments will become
apparent by reference to the drawings and by study of the following
descriptions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a graph of voltage versus time that illustrates a
representative fault voltage ride through requirements (both high
and low) for a wind turbine.
[0040] FIG. 2 is a schematic diagram of one embodiment of a wind
turbine that incorporates low voltage ride through utility.
[0041] FIG. 3A is a cross-sectional schematic representation of a
torque regulating gearbox that may be used by the wind turbine of
FIG. 2.
[0042] FIG. 3B is an exploded, perspective view of a hydrodynamic
torque converter used by the torque regulating gearbox of FIG.
3A.
[0043] FIG. 3C is a plan view of adjustable guide vanes, used by
the hydrodynamic torque converter of FIG. 3B, in a maximum open
position.
[0044] FIG. 3D is a plan view of the adjustable guide vanes, used
by the hydrodynamic torque converter of FIG. 3B, in a closed
position.
[0045] FIG. 4 is a flow diagram of one embodiment of a low voltage
ride through protocol for a wind FIG. 5 is a flow diagram of
another embodiment a low voltage ride through protocol for a wind
FIG. 6 is timing diagram that illustrates various waveforms
associated with a wind turbine during a low voltage ride through
condition.
DETAILED DESCRIPTION
[0046] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that it is not intended
to limit the invention to the particular form disclosed, but
rather, the invention is to cover all modifications, equivalents,
and alternatives falling within the scope and spirit of the
invention as defined by the claims.
[0047] FIG. 1 is a graph of voltage versus time that illustrates an
example of fault voltage ride through (FRT) requirements (including
high voltage ride through (HVRT) and low voltage ride through
(LVRT)) for a wind turbine. The FRT requirements are often measured
at a point of interconnection between a wind farm and a power grid,
rather than at an individual wind turbine. In this regard, even if
the voltage at the point of interconnection dips very low (e.g.,
0-15% of rated voltage), the voltage at the individual wind
turbines may be somewhat higher. As shown, a line 100 indicates a
HVRT requirement, while a line 102 indicates a LVRT requirement.
More specifically, to meet the FRT requirements, a generator is
required to remain connected to the power grid when the voltage of
the power grid (at the point of interconnection) is between the
HVRT line 100 and the LVRT line 102. The time period between time
To and time Ti may be set by a utility company or other
organization, and may have a value of 0.5 seconds, 0.625 seconds,
or 1 second, for example. In this example, a wind turbine would be
required to stay connected to the power grid if the voltage stays
at or above 15%, and dips down to 15% for no longer than Ti minus
To seconds. It should be appreciated that the VRT requirement shown
in FIG. 1 is only one example of many FRT requirements that may be
imposed by utility companies, standards organizations, countries,
or the like. For example, generators may be required to stay
connected to a power grid when the voltage at the point of
interconnection dips down to 0% for a period of time.
[0048] FIG. 2 is a schematic diagram of one embodiment of a wind
turbine 200 that may be configured to provide low voltage ride
through functionality. In operation, wind imparts energy to the
blades 201 of a wind rotor 202, which in turn imparts a mechanical
torque onto a shaft of a synchronous generator 214. The synchronous
generator 214 is coupled directly to a power grid 224 to provide
power to customers using the power grid 224. To adjust and control
the rotational speed and torque applied to the synchronous
generator 214, a fixed 2-stage mechanical gearbox 204 and a
torque-regulating gearbox (TRG) 210 are disposed between the
synchronous generator 214 and the wind rotor 202. Further, a
turbine control system module 236 and a TRG control system module
228 may be provided to monitor and control the various functions of
the wind turbine 200. Each of the various components of the wind
turbine 200 is described in greater detail below.
[0049] In one embodiment, the synchronous generator 214 is a 2
Megawatt (MW), 4 pole self-excited synchronous generator that
operates at a constant frequency of 1800 RPM for 60 Hz power
systems (1500 RPM for 50 Hz power systems), although other
synchronous generators may be utilized. An Automatic Voltage
Regulator (AVR) 216 may be coupled to the synchronous generator 214
to provide voltage control, power factor control, synchronization
functions, and the like. Advantageously, since the synchronous
generator 214 is directly connected to the power grid 224, the need
for complex power electronics to condition or transform the power
may be eliminated. As can be appreciated, any suitable method may
be used for the excitation of the synchronous generator 214. In one
embodiment, the excitation system includes a pilot exciter, which
may include a permanent magnet generator (PMG). Advantageously,
this configuration may eliminate the requirement of an outside
power supply to provide excitation, as well as eliminating the need
for slip rings and/or brushes, which may reduce the maintenance
requirements of the synchronous generator 214.
[0050] Because the synchronous generator 214 is directly coupled to
the power grid 224, the dynamic behavior of the wind turbine 200 is
partially determined by the rotational speed of the rotor shaft of
the synchronous generator 214 and the frequency of the power grid
224 being absolutely fixed. That is, the energy captured from the
wind must be processed between the wind rotor 202 and the
synchronous generator 214. Therefore, one major design requirement
is that the mechanical driving torque of the synchronous generator
214 should have a large enough safety margin with respect to the
electrical pull-out torque. This requirement may be met by
providing the synchronous generator 214 with suitable physical
characteristics, by providing a torsional compliance and damping in
the mechanical drive train, and by providing other techniques
described herein.
[0051] As noted above, since the rotor speed of the synchronous
generator 214 is fixed to the frequency of the power grid 224 and
the wind speed is variable, the TRG 210 is provided to convert the
torque and speed of the shaft of the wind rotor 202 to a form
suitable for the synchronous generator 214. The TRG 210 may be of
any appropriate configuration, for instance the TRG 210 may be in
the form of a superimposition gearbox of any of a number of
configurations. In one embodiment, the TRG 210 is a combination of
a torque converter and a planetary gear system. A representative
configuration for the TRG 210 is the WinDrive.RTM. available from
Voith Turbo GmbH and Co. KG, having a place of business in
Heidenheim, Germany. One or more features that may be used in
relation to the TRG 210 are disclosed in U.S. Patent Application
Publication Nos.: U.S. 2005/0235636, entitled "Hydrodynamic
Converter," and published on Oct. 27, 2005; U.S. 2005/0194787,
entitled "Control System for a Wind Power Plant With Hydrodynamic
Gear," and published on Sep. 8, 2005; and U.S. 2008/0197636,
entitled "Variable-Speed Transmission for a Power-Generating," and
published on Aug. 21, 2008, the entire disclosure of these three
published applications being incorporated by reference herein.
[0052] The TRG 210 may be characterized as being disposed in a
drive train that extends between the wind rotor 202 and the
synchronous generator 214 (e.g., the drive train transferring the
rotation of the wind rotor 202 to the synchronous generator 214).
Any appropriate type of torque regulator or torque-regulating
device/system may be utilized in place of the TRG 210 (in which
case the above-noted TRG control system module 228 may also be
referred to as a "torque regulator control system module 228"). The
torque regulator or torque-regulating device/system may be
incorporated in any appropriate manner in relation to the drive
train that extends between the wind rotor 202 and the synchronous
generator 214 (e.g., at one or more locations). Any appropriate way
of regulating the torque transfer between the wind rotor 202 and
the synchronous generator 214 may be utilized (e.g., electrically,
hydraulically).
[0053] In one embodiment shown in FIGS. 3A-3D, the TRG 210 includes
a combination of a hydraulic or hydrodynamic torque converter 602,
and a 2-stage functionally interconnected revolving planetary gear
system 604 positioned between the 2-stage mechanical gearbox 204
and the synchronous generator 214. In the revolving planetary gear
system 604, input power from an input shaft 606 (which is rotatably
driven by rotation of the wind rotor 202) is supplied to a carrier
608 of the left stage of the revolving planetary gear system 604. A
plurality of planetary gears 610 are rotatably mounted on the
carrier 608. Any appropriate number of planetary gears 610 may be
utilized. Simultaneously, a hydrodynamic circuit drives the outer
annulus (ring) gear 616 via a control drive.
[0054] In most planetary gear systems, one of the three elements
(i.e., planet gear carrier, ring gear, or sun gear) is fixed. In
the TRG 210 however, all three elements of the left stage of the
revolving planetary gear system 604 may rotate. Between the annulus
gear 616 and the fluid-machine it may be necessary to adapt speed
and direction of rotation by means of a fixed gear stage 614. The
revolving planetary gear system 604 leads both power flows via a
sun gear 618 to an output shaft 612 that connects to the
synchronous generator 214. In the hydraulic circuits, control power
is taken from the output shaft 612 with a pump wheel 620 of the
hydrodynamic torque converter 602 and returned to the revolving
planetary gear system 604 via a turbine wheel 622 of the
hydrodynamic torque converter 602. Power flow in a variable speed
gear unit can vary continuously by an interacting combination of
the revolving planetary gear system 604 and the hydrodynamic torque
converter 602.
[0055] The hydrodynamic torque converter 602 is provided with
adjustable guide vanes 624 (incorporated by a guide vane housing
626) and can thus be used as an actuator or control variable for
the power consumption of the pump wheel 620. The energy content of
the fluid and torque generated by the turbine wheel 622 varies with
changes in pump wheel 620 power consumption. Rotation of the
turbine wheel 622 is at least in part dictated or otherwise
controlled by the position of the guide vanes 624. FIG. 3C shows
the guide vanes 624 in the maximum open position (which would allow
the turbine wheel 622 to rotate at a maximum speed under current
conditions). FIG. 3D shows the guide vanes 624 in the closed
position.
[0056] Adjusting the position of the guide vanes 624 between the
open position (FIG. 3C) and closed position (FIG. 3D) controls the
rotational speed of the turbine wheel 622, as well as the energy
"absorbed" by the hydrodynamic torque converter 602.
[0057] The heart of a hydrodynamic torque converter 602 is its
hydraulic circuit; including the pump wheel 620, turbine wheel 622,
and a guide wheel or guide vane housing 626 with adjustable guide
vanes 624. These components are combined in a common housing that
contains hydraulic oil or any other appropriate fluid of an
appropriate viscosity. A flow path of hydraulic fluid in the common
housing is shown schematically in FIG. 3B and is identified by
reference numeral 621. The mechanical energy of the input shaft 606
is converted into hydraulic energy through the pump wheel 620. In
the turbine wheel 622, the same hydraulic energy is converted back
into mechanical energy and transmitted to the output shaft 612. The
adjustable guide vanes 624 of the guide wheel 626 regulate the mass
flow in the hydraulic circuit. When the guide vanes 624 are closed
(i.e., low mass flow; FIG. 3D), the power transmission is at its
minimum. When the guide vanes 624 are completely open (i.e., large
mass flow; FIG. 3C), the power transmission is at its maximum.
Because of the change in mass flow (due to the adjustable guide
vanes 624), the speed of the turbine wheel 622 can be adjusted to
match the various operating points of the synchronous generator
214.
[0058] In operation and referring now to both FIG. 2 and FIGS.
3A-3D, the TRG control system module 228 of the wind turbine 200
may control the positioning of the guide vanes 624 of the TRG 210
so that the rotational speed and torque of the rotor shaft of the
synchronous generator 214 is suitably controlled. In this regard,
the TRG control system module 228 may communicate with the turbine
control system module 236 to achieve this function. The control
system modules 228 and 236 may be physically or logically isolated,
or may be combined into a single unit. Further, the control system
modules 228 and 236 may be implemented in hardware, software, a
combination thereof, or in any appropriate manner. As an example,
the control system modules 228 and 236 may be implemented in one or
more "off-the-shelf" or customized microcontrollers.
[0059] Although one example of the TRG 210 is described above,
again it should be appreciated that any suitable configuration
(e.g., any torque-regulating device (TRD)) may be provided to
convert the torque and speed of the shaft of the wind rotor 202 to
a form suitable for the synchronous generator 214. As an example, a
TRD that includes electrical mechanisms (as opposed to hydraulic)
to regulate the torque and/or speed of the shaft of the wind rotor
202 may be used.
[0060] The wind turbine 200 of FIG. 2 again includes a wind rotor
202 that in turn includes a plurality of rotor blades 201 (e.g.,
three rotor blades) that may be designed for optimum aerodynamic
flow and energy transfer. Any appropriate number of rotor blades
201 may be utilized. Further, the wind rotor 202 may include a
pitch control system that is operable to adjust the angle of the
rotor blades 201 in a desired/required manner. To achieve this
functionality, the wind rotor 202 may include a hydraulic pitch
control system that includes pitch valves 234 that are controllable
by the turbine control system module 236. The position or pitch of
the rotor blades 201 could be simultaneously or collectively
adjusted, or could be independently adjusted.
[0061] In addition to pitch control, the wind turbine 200 of FIG. 2
may also include controllable yaw drives 232 that are operable to
adjust the direction that the wind turbine 200 faces (specifically
the direction
[0062] that the wind rotor 202 faces). For example, the turbine
control system module 236 may control the yaw drives 232 to rotate
the wind rotor 202 and its rotor blades 201 to face into the
direction of the wind, such that the efficiency of the wind turbine
200 may be optimized.
[0063] The wind turbine 200 may also include an uninterruptable
power supply (UPS) 230. The UPS 230 may be coupled to various
components (e.g., the pitch valves 234, the control system modules
228 and 236, and the like) and functions to provide power to the
components, especially when a main source of power is not
available. The UPS 230 may include any type of power system,
including one or more batteries, photovoltaic cells, capacitors,
flywheels, and the like.
[0064] The wind turbine 200 may also include a controllable
mechanical brake 206 coupled between the 2-stage gearbox 204 and
the TRG 210. The brake 206 may be controlled by the turbine control
system module 236 to reduce the rotational speed of the wind rotor
202. It should be appreciate that any suitable braking mechanism
may be used, including but not limited to tip brakes, ailerons,
spoilers, boundary layer devices, and the like. One or more brakes
of any appropriate type may be included in the drive train between
the wind rotor 202 and the synchronous generator 214, for instance
so as to be disposed between the wind rotor 202 and the TRG 210. In
addition, friction clutches 208 and 212 may be disposed in the
mechanical drive train to limit the torque applied between
components and to selectively couple and decouple the various
shafts of the drive train components.
[0065] As can be appreciated, before the synchronous generator 214
is coupled directly to the power grid 224, certain conditions must
be met. For example, the stator voltage of the synchronous
generator 214 must substantially match the voltage of the power
grid 224, and the frequency and phase of the voltages must match as
well. To achieve this functionality, a synchronization unit 218, a
grid measurement unit 226, and a circuit breaker 222 may be
provided for the wind turbine 200. In operation, the
synchronization unit 218 may communicate with the AVR 216 and the
control system modules 236 and 228 to adjust the voltage
characteristics of the synchronous generator 214 to match those of
the power grid 224 as measured by the grid measurement unit 226.
Once the voltage characteristics substantially match on both the
generator side and the power grid side, the synchronization unit
218 may send a command to the circuit breaker 220 to close the
circuit, thereby coupling the synchronous generator 214 to the
power grid 224. The circuit breaker 222 may also be coupled to a
grid and generator protection unit 220 that is operative to sense
harmful conditions where it may be desirable to disconnect the wind
turbine 200 from the power grid 224.
[0066] FIG. 4 is a flow diagram 300 of one embodiment of a process
or protocol for low voltage ride through in the wind turbine 200.
It should be appreciated that the steps described herein may be
executed in various sequential orders, or concurrently. Further,
some embodiments of an exemplary LVRT process may include a subset
or all of the steps. In discussing the flow diagram 300, various
components of the wind turbine 200 of FIGS. 2 and 3A-3D may be
addressed. The functionality embodied by the flow diagram 300 may
be implemented by the wind turbine 200 in any appropriate manner
(e.g., utilizing one or both of the control system modules 236,
228)
[0067] Initially, the wind turbine 200 may detect a low voltage
event condition (step 302). For example, the grid measurement unit
226 may sense the existence of a low voltage on the power grid 224,
and then provide an indication to the turbine control system module
236. Such an indication may include asserting a "low voltage
detect" signal. Once a low voltage condition has been detected, the
wind turbine 200 may then use a variety of techniques that enable
the synchronous generator 214 to remain coupled directly to the
power grid 224 during the low voltage event.
[0068] Immediately after the low voltage event has been detected,
the AVR 216 may be controlled to boost the excitation current
applied to the rotor winding of the synchronous generator 214 (step
304). This has the effect of increasing the rotor field energy,
which in turn supports the voltage at the stator of the synchronous
generator 214 during the low voltage event by boosting the reactive
power. By sustaining the stator voltage, the unbalance between the
mechanical torque (from the wind) and the reduced electrical torque
(from the grid 224) should be minimized.
[0069] As noted above, when a low voltage event occurs, there will
be an unbalance between the mechanical torque and the electrical
torque due to the rapid decrease of the voltage level at the stator
of the synchronous generator 214. To further minimize this
unbalance, the turbine control system module 236 and the TRG
control system module 228 may operate to rapidly adjust the
position of the guide vanes 624 of the TRG 210 to limit the
mechanical torque increase applied to the shaft of the synchronous
generator 214 (step 306).
[0070] As can be appreciated, by reducing the torque on the
generator side of the TRG 210, the excess torque on the wind rotor
202 side will tend to accelerate the wind rotor 202. To limit the
acceleration of the wind rotor 202, the turbine control system
module 236 may apply mechanical brake 206 to the output shaft of
the 2-stage gearbox 204 (step 308). The brake system may be
designed to continuously control the brake torque to minimize the
aforementioned torque imbalance during the low voltage event. In
one embodiment, the brake 206 may be applied with a force that is
proportional to the voltage of the power grid 224 (e.g., measured
by the grid measurement unit 226). Additionally, the brake 206 may
be applied with a force that is dependent upon a speed or
acceleration characteristic of the wind rotor 202.
[0071] To further limit the acceleration of the wind rotor 202
caused by the guide vane 624 adjustment (step 306), the blade
angles or pitch of the blades 201 of the wind rotor 202 may be
adjusted (step 310). This has the effect of decreasing the torque
of the blades 201 (e.g., reducing the torque the wind exerts on the
rotor blades 201), thereby reducing the input energy from the wind
to the wind turbine 200, which reduces the acceleration of the
shaft of the wind rotor 202.
[0072] During the low voltage event, various components of the wind
turbine 200 also may be isolated from the event by the turbine
control system module 236 to reduce the potential of harm to such
various components. For example, the yaw drives 232 and any
hydraulic pumps may be isolated to prevent uncontrolled motor trip
conditions that may otherwise be caused by the low voltage event
(step 312).
[0073] FIG. 5 is a flow diagram 400 of one embodiment of a process
or protocol for returning the wind turbine 200 to normal operation
following a low voltage event. Again, this discussion may refer to
certain components of the wind turbine 200 of FIGS. 2 and 3A-3D.
The functionality embodied by the flow diagram 400 may be
implemented by the wind turbine 200 in any appropriate manner
(e.g., utilizing one or both of the control system modules 236,
228).
[0074] Initially for the case of the flow diagram 400, the wind
turbine 200 may detect that the voltage level of the grid 224 is at
an acceptable level (e.g., greater than 70% of the rated voltage)
(step 402). Then, steps may be taken to return the wind turbine 200
to its normal operating state. Similar to the steps shown and
described in FIG. 4, the steps of FIG. 5 may be performed in any
sequential order, or concurrently with each other.
[0075] At step 404, the AVR 216 of the wind turbine 200 may be
controlled to reduce the exciter current in the rotor winding of
the synchronous generator 214 from its boosted level to a nominal
level. Further, the position of the guide vanes 624 of the TRG 210
may be resumed or returned to their normal operating position (step
406). To release the limit on the acceleration of the wind rotor
202, the mechanical brake 206 may be disengaged (step 408), and the
blade angles of the rotor blades 201 may be restored to their
normal operation (step 410). Additionally, the electrical
peripherals that were isolated in step 312 of FIG. 4 may be
returned to their normal operating conditions (step 412).
[0076] FIG. 6 is timing diagram 500 that illustrates various graphs
associated with the wind turbine 200 during the LVRT process
described above. Initially, the representation for each graph is
described. The graph 502 represents the voltage at the stator of
the synchronous generator 214 as a percentage of the rated voltage.
The graph 504 represents a "low voltage detect" signal that is
asserted when the wind turbine 200 detects a low voltage event. The
graph 506 represents the exciter current (per unit) that is applied
to the rotor winding of the synchronous generator 214. The graph
508 represents the current (per unit) at the stator of the
synchronous generator 214. The graph 510 represents the position
(per unit) of the guide vanes 624 of the TRG 210. The graph 512
represents the force (per unit) applied to the mechanical brake
206. The graph 514 represents the blade angle in degrees of the
rotor blades 201. Finally, the graph 516 represents the drive train
speed (per unit).
[0077] As shown in the graph 502, the low voltage event occurs at
time to, causing the stator voltage to fall to 15% of the rated
voltage. As a result, the wind turbine 200 asserts the "low voltage
detect" signal, as shown in graph 504. Once the "low voltage
detect" signal has been asserted, the wind turbine control system
module 236 may activate the various processes described above with
reference to FIG. 4. More specifically, the exciter current may be
boosted (graph 506), the position of the guide vanes 624 may be
adjusted (graph 510), the mechanical brake 206 may be applied
(graph 512), and the blade angles of the blades 201 of the wind
rotor 202 may be adjusted (graph 514), or any combination
thereof.
[0078] The graph 516 illustrates the speed of the mechanical drive
train during the low voltage event. As shown, the drive train speed
increases almost immediately after the low voltage event due to the
excess mechanical torque caused by the movement of the guide vanes
624 of the TRG 210 (see step 306 shown in FIG. 4). Then, as the
brake 206 and the blade angles are adjusted, the speed of the drive
train is reduced through the end of the low voltage event, which
occurs at time t3. After the voltage at the power grid 224 has been
restored, the control system modules 228 and 236 control the
operation of the wind turbine 200 to restore the drive train speed
back to a nominal speed, as indicated by the arrow 520 shown in the
graph 516.
[0079] As shown in the graph 508, the stator current of the
synchronous generator 214 rises rapidly at the onset of the low
voltage event. This occurs because the large sudden voltage drop
causes a large short-circuit torque in the air-gap of the
synchronous generator 214. This air-gap torque may be limited
naturally by the torsional stiffness of the shaft, and also by the
friction clutch 212 disposed between the synchronous generator 214
and the TRG 210.
[0080] At time t.sub.3, the wind turbine 200 detects that the
voltage has recovered to an acceptable level (e.g., 70% of rated
voltage), and the turbine control system module 236 may then
execute steps to return the wind turbine 200 to a normal operating
state (see FIG. 5). As shown in the graph 510, the blade angles may
be returned to their operating position (see the arrow 518). In one
embodiment, the blade angles are adjusted at a rate that is
programmable and defined by the speed-torque characteristics of the
wind turbine 200. Similarly, the excitation current, the brake 206,
and the blade angles of the wind rotor 202 may be restored to their
normal operating conditions, as shown in the graphs 506, 512, and
514, respectively.
[0081] In addition to the aforementioned techniques, the
synchronous generator 214 itself may be designed and configured to
increase the LVRT capabilities of the wind turbine 200. For
example, in one embodiment, the dynamic pull-out torque is
maximized by providing a synchronous generator 214 with a
relatively low sub-transient reactance and a low d-axis open
circuit transient time constant. In this regard, the synchronous
generator 214 may be capable of remaining connected to the power
grid 224 when the unbalance of mechanical and electrical torque is
relatively high.
[0082] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description is to be considered as exemplary and not
restrictive in character. For example, certain embodiments
described hereinabove may be combinable with other described
embodiments and/or arranged in other ways (e.g., process elements
may be performed in other sequences). Accordingly, it should be
understood that only the preferred embodiment and variants thereof
have been shown and described and that all changes and
modifications that come within the spirit of the invention are
desired to be protected.
* * * * *